Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversion. Certain zeolitic materials are ordered, porous crystalline aluminosilicates having a definite crystalline structure as determined by X-ray diffraction, within which there are a large number of smaller cavities which may be interconnected by a number of still smaller channels or pores. These cavities and pores are uniform in size within a specific zeolitic material. Since the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as "molecular sieves" and are utilized in a variety of ways to take advantage of these properties.
Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline silicates. These silicates can be described as a rigid three-dimensional framework of SiO.sub.4 and Periodic Table Group IIIA element oxide, e.g. AlO.sub.4, in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total Group IIIA element, e.g. aluminum, and silicon atoms to oxygen atoms is 1:2. The electrovalence of the tetrahedra containing the Group IIIA element, e.g. aluminum, is balanced by the inclusion in the crystal of a cation, for example an alkali metal or an alkaline earth metal cation. This can be expressed wherein the ratio of the Group IIIA element, e.g. aluminum, to the number of various cations, such as Ca/2, Sr/2, Na, K or Li, is equal to unity. One type of cation may be exchanged either entirely or partially with another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it has been possible to vary the properties of a given silicate by suitable selection of the cation. The spaces between the tetrahedra are occupied by molecules of water prior to dehydration.
The catalytic cracking of hydrocarbon oils using zeolites is a known process, practiced, for example, in fluid-bed catalytic cracking (FCC) units, moving bed or Thermofor Catalytic Cracking (TCC) reactors and fixed bed crackers. Zeolites have been found to be particularly effective for the catalytic cracking of a gas oil to produce motor fuels and have been described and claimed in many patents including U.S. Pat. Nos. 3,140,249; 3,140,251; 3,140,252; 3,140,253; and 3,271,418. It is also known in the art to incorporate the crystalline zeolite into a matrix for catalytic cracking and such disclosure appears in one or more of the above-identified U.S. patents.
Crystalline materials having the X-ray structure of MCM-22 are useful in catalytic cracking to increase the total gasoline yield and octane, see U.S. Pat. Nos. 4,983,276 and 5,039,640, herein incorporated by reference.
It is desirable to improve the hydrothermal stability of the catalysts which are based upon porous crystalline materials having the X-ray diffraction pattern shown in Table 1 of the specification to increase the activity that the catalyst maintains after repeated cycles of steaming such as is experienced in the FCC process.